% First summand in core function
% Usage: y = func_1(q, zeta, m, CONSTS)

function y = func_1(q, zeta, m, CONSTS)
    k0 = CONSTS.k0;
    a  = CONSTS.a;
      
    %y = besselj(m+1, k0*a*q).^2 .* exp(-k0*q*zeta);
    y = besselmx(double('J'), m+1, k0*a*q, 0).^2 .* exp(-k0*q*abs(zeta));
end
